1. Field of the Invention
This invention relates to an image processing method and apparatus and, by way of example, to an image processing method and apparatus for modulating image data and adding specific information to the image data.
2. Description of the Related Art
The recent improvement in the capabilities and performance of color copying machines and color printers has been accompanied by an increase in the crime of counterfeiting bank notes and securities by making unlawful use of these devices.
In order to prevent such crime, techniques have been proposed in which data relating to an image pattern corresponding to a specific original is registered beforehand in a color copying machine or color printer itself and unlawful copying if is forcibly inhibited when this data is identified. For example, see the specification of U.S. Ser. No. 07/351,165, filed on May 12, 1989.
However, with this method of preventing counterfeiting, there is a limitation upon the number of image patterns capable of being registered, and therefore it is impossible to prevent the counterfeiting of all types of bank notes and securities.
Further, in a color copying machine and color printer having an external interface, there are cases in which such a counterfeiting preventing circuit will not function. For example, if the image data sent from the external interface has a format in which the items of the three primary colors of red (R), green (G) and blue (B) arrive substantially simultaneously pixel by pixel, the aforementioned counterfeiting preventing circuit is capable of operating. However, if the image data has a data format made to conform to the individual characteristics of the printer, as in the manner of cyan (C), magenta (M), yellow (Y) and black (K), the reproducible combinations of colors are plural in number. This necessitates a plurality of image patterns for the purpose of making decisions, the decisions for preventing counterfeiting become very complicated to make and the number of images capable of being judged diminish. Furthermore, in a case where the image data of each color component is sent field-sequentially color by color, the image data must be stored in memory in order for the image to be judged. This results in higher equipment cost and makes it very expensive to effect the judgments needed to prevent counterfeiting.
Further, even if the foregoing problem relating to an image signal from an external interface is solved, this will not make it possible to avoid a picture closely resembling a registered bank note from being judged erroneously as being a bank note or a soiled bank note from being judged erroneously as not being a bank note.
With this as a background, the applicant has already proposed (see U.S. Ser. No. 07/856,996 filed on Mar. 24, 1992) a technique through which information capable of specifying a copying machine or the person making a copy is added to the reproduced image. More specifically, the image signal is modulated by a pattern of numerals or symbols, such as the manufacturing number of the copying machine, with regard to a color component (yellow, for example) least noticeable to the human eye, this color being selected from among the output color components (e.g., magenta, cyan, yellow, black) of the copying machine.
However, even though yellow is the output color component most difficult for the eye to see, the effect upon the image when the image signal is modulated cannot be ignored in the technique described above. In particular, when a color copying machine is used in design-related applications, an impediment encountered is that patterns not present in the original are brought into view. In a case where an image in a host computer is printed out using the external interface of the color copying machine, it is possible to directly output computer graphics and, hence, uniform areas are likely at the image signal level. If the yellow component is modulated at such time, added patterns become readily conspicuous at portions that are a uniform light gray or light blue.
Further, in a method in which a pattern is represented by units that are a collection of several numerals or characters and all added patterns are constructed by repeating this unit pattern at a fixed interval, a problem that arises is that the patterns become readily conspicuous because they are gathered closely together. In addition, since the human eye recognizes regular patterns such as the above-mentioned added patterns more easily than patterns in a random array, the patterns become even more noticeable when they are placed on a lattice. If the degree of modulation of the image signal is reduced in an effort to solve these problems, the added patterns may not be read, depending upon the specific originals.
Accordingly, there is a need for a modulating method and measures for dealing with patterns that satisfy contradictory requirements, namely a requirement that copies of certain originals such as bank notes be made positively identifiable as copies through some method and a requirement that such identification not be readily apparent to the eye in all output images.